HMD65 can be accessed with the Modbus and BACnet protocols over the RS-485 interface. The protocol selection and communication settings for either protocol are entered with the DIP switches on the HMD65 component board (see Figure 1).
The Modbus variant used in HMD65 is Modbus RTU. For a list of the Modbus registers available in HMD65, see Modbus Registers.
The BACnet variant used in HMD65 is BACnet MS/TP. For a description of the HMD65 BACnet implementation, see BACnet Reference.
Setting Device MAC Address with DIP Switches
Modbus and BACnet MAC Address Ranges
The BACnet MS/TP MAC address range for the transmitter is 0 … 127 (master mode only).
The Modbus RTU MAC address range for the transmitter is 1 … 247.
Configuring an address above the range maximum results in the address defaulting back to the maximum address (127 or 247). Addresses below the range minimum default to the minimum address (0 or 1).
Bit Rate and Parity Options
- The bit rate 4800 is used only for Modbus RTU (use 9600 and above for BACnet MS/TP).
- If the bit rate DIP switches are all
set to OFF (left), the following defaults are used:
- Modbus RTU: 19200
- BACnet MS/TP: 38400
- The parity selection (N/E) only has an effect on Modbus RTU communication.